> The SPA broke it... Back button broken and a buggy custom implementation is there instead? Check.
MPAs break back buttons all the damn time, I'd say more often than SPAs do.
Remember the bad old days when websites would have giant text "DO NOT USE YOUR BROWSER BACK BUTTON"? That is because the server had lots of session state on it, and hitting the browser back button would make the browser and server be out of sync.
Or the old online purchase flows where going back to change the order details would completely break the world and you'd have to re-enter all your shipping info. SPAs solve that problem very well.
Let's think about it a different way.
If you are making a phone app, would you EVER design it so that the app downloads UI screens on demand as the user explores the app? That'd be insane.